A typical shutter mechanism of the prior art includes an electromagnet comprising a ferrite core surrounded by a magnetic winding on a pancake bobbin and also includes a very thin elongated flexible foil steel strip attached by retaining screws at one end to a collar and lying parallel to and below a laser beam path when the electromagnet is inactive. In operation, the winding is energized, activating the magnet and causing the free end of the foil strip to be attracted to the magnet and bend upward into the beam path. As the end of the strip intercepts the beam path, the beam is reflected away from the path by a few degrees. The angle of reflection increases as the foil end approaches the magnet. In the fully closed position the strip conforms flat against the magnet and then bends sharply downward to the retaining screws, blocking the beam.
The foil strip is not only extremely flexible, but also has low mass, which aids in reducing vibration caused by the collision of the strip with the electromagnet. However, the strip is also very weak, particularly at stress points in the bend, and thereby has a lifetime of only about 100,000 cycles before breakage occurs. The strip reflects the beam at an angle near that of the unaltered beam path, creating an unwanted stray reflection line that must be trimmed off. The orientation of the strip in the fully closed position allows laser light to be scattered back into the laser, preventing its use in certain applications. Thermally, the thin foil is not capable of conducting away sufficient heat arising from absorption of high power laser light.
In U.S. Pat. No. 4,799,767, Woodruff describes a shutter mechanism having a stiff, but still flexible, ferromagnetic blade mounted in V-shaped relationship with the poles of an electromagnet. The electromagnet has a cylindrical core with a lengthwise, i.e. axial, slice defining poles, and has a toroidal winding around the core communicating with an electrical power supply. When the electromagnet is activated, the free end of the blade flexes toward the magnetic pole surfaces. In one embodiment, the light path passes between the magnetic poles, and the blade, normally parallel to the beam path, flexes downward to block the beam. The flexed blade and a light absorptive backup plate, against which the blade normally rests, combine to define a V-shaped light trap for the beam. In another embodiment, the blade normally lies at an angle in the lengthwise direction across the beam path and rests against a backup plate, covering an opening in the plate. A light absorptive tongue between the electromagnet's poles combines with the blade to form a light trap. When the blade flexes downward, the light passes through the opening in the backup plate. In both embodiments, the beam path is directed generally along the length of the blade.
An object of the present invention is to produce a laser beam shutter mechanism having long life and no stray reflection so as to be suitable for high speed pulse operation.
Another object of the present invention is to produce a shutter mechanism suitable for use with high power lasers and other beam sources.